fix(mcp): avoid Chroma open when cached DB disappears

mempalace/mcp_server.py

@@ -164,10 +164,10 @@ def _get_result_ids(result) -> list:
     if ids is not None:
         return ids
     if isinstance(result, dict):
-        return result.get("ids", [])
+        return result.get("ids") or []
     getter = getattr(result, "get", None)
     if callable(getter):
-        return getter("ids", [])
+        return getter("ids") or []
     return []
 
 
@@ -361,6 +361,7 @@ def _force_chroma_cache_reset() -> None:
         _palace_db_mtime, \
         _metadata_cache, \
         _metadata_cache_time
+    cached_client = _client_cache
     _client_cache = None
     _collection_cache = None
     _collection_cache_backend = None
@@ -376,7 +377,24 @@ def _force_chroma_cache_reset() -> None:
         backend = get_backend_for_palace(_config.palace_path)
         backend.close_palace(PalaceRef(id=_config.palace_path, local_path=_config.palace_path))
     except Exception:
-        pass
+        logger.debug("Failed to close cached Chroma backend during cache reset", exc_info=True)
+    if cached_client is not None:
+        try:
+            close = getattr(cached_client, "close", None)
+            if callable(close):
+                close()
+        except Exception:
+            logger.debug(
+                "Failed to close MCP-local Chroma client during cache reset", exc_info=True
+            )
+    try:
+        from chromadb.api.client import SharedSystemClient
+
+        clear_system_cache = getattr(SharedSystemClient, "clear_system_cache", None)
+        if callable(clear_system_cache):
+            clear_system_cache()
+    except Exception:
+        logger.debug("Failed to clear Chroma shared system cache during cache reset", exc_info=True)
 
 
 # ── Vector-search disabled flag (#1222) ──────────────────────────────────
@@ -687,6 +705,16 @@ def _get_collection(create=False):
                 }
         return None
 
+    db_path = os.path.join(_config.palace_path, "chroma.sqlite3")
+    if not create and not os.path.isfile(db_path):
+        _force_chroma_cache_reset()
+        _collection_open_error = {
+            "error": "Chroma database missing",
+            "details": f"Could not open missing database at {db_path}.",
+            "hint": "Run: mempalace status or mempalace repair-status for diagnostics.",
+        }
+        return None
+
     for attempt in range(2):
         try:
             if _collection_cache is not None and (

tests/test_mcp_server.py

@@ -1239,6 +1239,16 @@ class TestWriteTools:
         assert result["reason"] == "already_exists"
         mock_col.upsert.assert_not_called()
 
+    def test_get_result_ids_normalizes_none_to_empty_list(self):
+        from mempalace import mcp_server
+
+        class DictLikeResult:
+            def get(self, key, default=None):
+                return None
+
+        assert mcp_server._get_result_ids({"ids": None}) == []
+        assert mcp_server._get_result_ids(DictLikeResult()) == []
+
     def test_add_drawer_fails_when_readback_misses(self, monkeypatch, config, kg):
         _patch_mcp_server(monkeypatch, config, kg)
         from mempalace import mcp_server
@@ -2385,10 +2395,20 @@ class TestCacheInvalidation:
         if os.path.isfile(db_file):
             os.remove(db_file)
 
+        make_client_calls = []
+
+        def fail_if_make_client_called(path):
+            make_client_calls.append(path)
+            raise AssertionError("_get_collection(create=False) should not open missing Chroma DB")
+
+        monkeypatch.setattr(mcp_server.ChromaBackend, "make_client", fail_if_make_client_called)
+
         # Cache should be invalidated; _get_collection returns None
         # because the backend can't open a missing DB without create=True
-        mcp_server._get_collection()
+        assert mcp_server._get_collection() is None
         # The key assertion: the old cached collection was dropped
+        assert make_client_calls == []
+        assert mcp_server._collection_cache is None
         assert mcp_server._palace_db_inode == 0
         assert mcp_server._palace_db_mtime == 0.0